3.9. How AUTOLOAD Works

The AUTOLOAD mechanism, built into the definition of Perl packages, is simple to use. If a subroutine named AUTOLOAD is declared within a package, it is called whenever an undefined subroutine is called within the package. AUTOLOAD is a special name, and must be capitalized as shown, because Perl is designed that way. Don't use the subroutine name AUTOLOAD (or DESTROY) for any other purpose, or you'll suffer unintended consequences.

Without an AUTOLOAD subroutine defined in a package, an attempt to call some undefined subroutine simply produces an error when the program runs. But if an AUTOLOAD subroutine is defined, it is called instead and is passed the arguments of the undefined subroutine. At the same time, the $AUTOLOAD variable is set to the name of the undefined subroutine.